A "jumble sale" is an event where people sell used items, like clothes or toys, at very low prices. It's like a big yard sale or a second-hand market. Full definition
It's a good idea to look out for anything educational at jumble sales, second hand bookshops and car boot sales. (home-ed.info)
The easy thing for me to do today would be to give you one of those sort of end of jumble sale speeches, where you say thank you to everyone, and say what a success it all was. (theguardian.com)
When I saw it hanging on the rack at a teeny jumble sale in North London I knew it was a gem and snatched it up immediately. (cutandchic.com)